Just got back from another trip up there. Was with the gf this time so had to stick to relatively tame stuff 🙂
We did the Braeval route from Kenny Wilson's book – nice and scenic but mostly pretty dull fire-road.
Persuaded the gf we should do one of the 'advanced' singletrack options on the route and were faced with a few km of pretty solid bog – not having much joy weaning the gf off trail centres, she was less than impressed!
Found a really nice little singletrack descent in the woods just above the David Marshall lodge in Aberfoyle on the way back down – they had signs up saying they were purpose built mtb trails. Only short but sweet and quite techy in places. Looked like there were a couple more but didn't get time to check them out.